iPhoto: THE “WHITE BALANCE” SECRET SETTING

You can set the white balance for any photo in iPhoto by entering Edit mode (click the Edit button at the bottom of the iPhoto window), then once you're in Edit mode, hold the Command key and click your cursor on something that's supposed to be light gray (that's right—don't click on something that's supposed to be white—click on something light gray). You'll see the Adjust panel appear, and the Temperature and Tint sliders (which control the white balance) will already be adjusted.